Solid Neon Research Articles

Coulomb Interaction-Driven Entanglement of Electrons on Helium

The generation and evolution of entanglement in many-body systems is an active area of research that spans multiple fields, from quantum information science to the simulation of quantum many-body systems encountered in condensed matter, subatomic physics, and quantum chemistry. Motivated by recent experiments exploring quantum information processing systems with electrons trapped above the surface of cryogenic noble gas substrates, we theoretically investigate the generation of entanglement between two electrons via their unscreened Coulomb interaction. The model system consists of two electrons confined in separate electrostatic traps that establish microwave-frequency quantized states of their motion. We compute the motional energy spectra of the electrons, as well as their entanglement, by diagonalizing the model Hamiltonian with respect to a single-particle Hartree product basis. We also compare our results with the predictions of an effective Hamiltonian. The computational procedure outlined here can be employed for device design and guidance of experimental implementations. In particular, the theoretical tools developed here can be used for fine-tuning and optimization of control parameters in future experiments with electrons trapped above the surface of superfluid helium or solid neon. Published by the American Physical Society 2024

Single-Electron Qubits Based on Quantum Ring States on Solid Neon Surface.

Single electrons trapped on solid-neon surfaces have recently emerged as a promising platform for charge qubits. Experimental results have revealed their exceptionally long coherence times, yet the actual quantum states of these trapped electrons, presumably on imperfectly flat neon surfaces, remain elusive. In this Letter, we examine the electron's interactions with neon surface topography, such as bumps and valleys. By evaluating the surface charges induced by the electron, we demonstrate its strong perpendicular binding to the neon surface. The Schrödinger equation for the electron's lateral motion on the curved 2D surface is then solved for extensive topographical variations. Our results reveal that surface bumps can naturally bind an electron, forming unique quantum ring states that align with experimental observations. We also show that the electron's excitation energy can be tuned using a modest magnetic field to facilitate qubit operation. This study offers a leap in our understanding of electron-on-solid-neon qubit properties and provides strategic insights on minimizing charge noise and scaling the system to propel forward quantum computing architectures.

Electronic absorption spectra of aniline cations in solid neon

Absorption spectrum of the electronic transition B2B1←X2B1 of aniline cation isolated in solid Ne at 3 K was recorded by using the newly-built mass-selective matrix isolation system. The observed broad vibronic transitions spanning between 23,000−28,000 cm−1 were assigned by the aid of quantum chemical calculations and Franck-Condon simulation. Quantum chemical calculations indicated noticeable changes in geometry between the ground state and the B state. This structural alteration activates low-frequency vibrational modes in combination with other vibrational modes, resulting in the broad appearance of this electronic transition.

Ab initio determination of melting and sound velocity of neon up to the deep interior of the Earth.

The thermophysical properties and elemental abundances of the noble gases in terrestrial materials can provide unique insights into the Earth's evolution and mantle dynamics. Here, we perform extensive abinitio molecular dynamics simulations to determine the melting temperature and sound velocity of neon up to 370GPa and 7500K to constrain its physical state and storage capacity, together with to reveal its implications for the deep interior of the Earth. It is found that solid neon can exist stably under the lower mantle and inner core conditions, and the abnormal melting of neon is not observed under the entire temperature (T) and pressure (P) region inside the Earth owing to its peculiar electronic structure, which is substantially distinct from other heavier noble gases. An inspection of the reduction for sound velocity along the Earth's geotherm evidences that neon can be used as a light element to account for the low-velocity anomaly and density deficit in the deep Earth. A comparison of the pair distribution functions and mean square displacements of MgSiO3-Ne and Fe-Ne alloys further reveals that MgSiO3 has a larger neon storage capacity than the liquid iron under the deep Earth condition, indicating that the lower mantle may be a natural deep noble gas storage reservoir. Our results provide valuable information for studying the fundamental behavior and phase transition of neon in a higher T-P regime, and further enhance our understanding for the interior structure and evolution processes inside the Earth.

Investigation of Isolated IrF5 -, IrF6 - Anions and M[IrF6] (M=Na, K, Rb, Cs) Ion Pairs by Matrix-Isolation Spectroscopy and Relativistic Quantum-Chemical Calculations.

The molecular IrF5 -, IrF6 - anions and M[IrF6] (M=Na, K, Rb, Cs) ion pairs were prepared by co-deposition of laser-ablated alkali metal fluorides MF with IrF6 and isolated in solid neon or argon matrices under cryogenic conditions. The free anions were obtained as well by co-deposition of IrF6 with laser-ablated metals (Ir or Pt) as electron sources. The products were characterized in a combined analysis of matrix IR spectroscopy and electronic structure calculations using two-component quasi-relativistic DFT methods accounting for spin-orbit coupling (SOC) effects as well as multi-reference configuration-interaction (MRCI) approaches with SOC. Inclusion of SOC is crucial in the prediction of spectra and properties of IrF6 - and its alkali-metal ion pairs. The observed IR bands and the computations show that the IrF6 - anion adopts an Oh structure in a nondegenerate ground state stabilized by SOC effects, and not a distorted D4h structure in a triplet ground state as suggested by scalar-relativistic calculations. The corresponding "closed-shell" M[IrF6] ion pairs with C3v symmetry are stabilized by coordination of an alkali metal ion to three F atoms, and their structural change in the series from M=Na to Cs was proven spectroscopically. There is no evidence for the formation of IrF7, IrF7 - or M[IrF7] (M=Na, K, Rb, Cs) ion pairs in our experiments.

Spectroscopic Identification of Trifluorosilylphosphinidene and Isomeric Phosphasilene and Silicon Trifluorophosphine Complex.

The perfluorinated silylphosphinidene, F3SiP, in the triplet ground state is generated by the reaction of laser-ablated silicon atoms with PF3 in solid neon and argon matrices. The reactions proceed with the initial formation of a silicon trifluorophosphine complex, F3PSi, in the triplet ground state, and a more stable inserted phosphasilene, FPSiF2, in the singlet ground state upon deposition. The trifluorosilylphosphinidene was formed through F-migration reactions of FPSiF2 and F3PSi following a two-state mechanism under irradiation with visible light (λ = 470 nm) and full arc light (λ > 220 nm), respectively. High-level quantum-chemical methods support the identification of F3PSi, FPSiF2, and F3SiP by matrix-isolation IR spectroscopy.

Quantum computing using floating electrons on cryogenic substrates: Potential and challenges

In this review, we introduce a developing qubit platform: floating-electron-based qubits. Electrons floating in a vacuum above the surface of liquid helium or solid neon emerge as promising candidates for qubits, especially due to their expected long coherence times. Despite being in the early stages, a variety of recent experiments from different groups have shown substantial potential in this role. We survey a range of theoretical proposals and recent experiments, primarily focusing on the use of the spin state as the qubit state, wherein the spin and charge states are hybridized. Throughout these proposals and experiments, the charge state is coupled to an LC resonator, which facilitates both the control and readout mechanisms for the spin state via an artificially introduced spin–charge coupling.

Spectroscopic Study of [Mg, H, N, C, O] Species: Implications for the Astrochemical Magnesium Chemistry.

Magnesium is an abundant metal element in space, and magnesium chemistry has vital importance in the evolution of interstellar medium (ISM) and circumstellar regions, such as the asymptotic giant branch star IRC+10216 where a variety of Mg compounds bearing H, C, N, and O have been detected and proposed as the important components in the gas-phase molecular clouds and solid-state dust grains. Herein, we report the formation and infrared spectroscopic characterization of the Mg-bearing molecules HMg, [Mg, N, C], [Mg, H, N, C], [Mg, N, C, O], and [Mg, H, N, C, O] from the reactions of Mg/Mg+ and the prebiotic isocyanic acid (HNCO) in the solid neon matrix. Based on their thermal diffusion and photochemical behavior, a complex reactivity landscape involving association, decomposition, and isomerization reactions of these Mg-bearing molecules is developed, which can not only help understand the chemical processes of the magnesium (iso)cyanides in astrochemistry but also provide implications on the presence of magnesium (iso)cyanates in the ISM and the chemical model for the dust grain surface reactions. It also provides a new paradigm of the key intermediate nature of the cationic complexes in the formation of neutral interstellar species.

Synthesis and characterization of azaborepin radicals in solid neon through boron-mediated C-N bond cleavage of pyridine.

The reactivity of pyridine is a complex topic due to its unique electronic structure. The reactions of atomic boron with pyridine molecules in solid neon have been investigated using matrix isolation infrared absorption spectroscopy. Three products (marked as A, B, and C) were observed and characterized through 10B, D and 15N isotopic substitution pyridine regents as well as quantum chemical calculations. In the reaction, the ground-state boron atom can attack the lone pair electrons of the nitrogen atom in the pyridine molecule, resulting in the formation of a 1-boropyridinyl radical (A). Alternatively, addition to the aromatic π-system of pyridine can occur in a [1,4] type, leading to the formation of a B[η2(1,4)-C5H5N] complex (B). Under UV-visible light (280 < λ < 580 nm) irradiation, these two compounds can further undergo photo-isomerization to form BN-embedded seven-membered azaborepin compounds (C). The observation of species A, B, and the subsequent photo-isomerization to species C is consistent with theoretical predictions, indicating that these reactions are kinetically favorable. This research provides valuable insights into the future design and synthesis of corresponding BN heterocyclic derivatives.

Beryllium Dimer Reactions with Acetonitrile: Formation of Strong Be-Be Bonds.

Laser ablated Be atoms have been reacted with acetonitrile molecules in 4 K solid neon matrix. The diberyllium products BeBeNCCH3 and CNBeBeCH3 have been identified by D and 13C isotopic substitutions and quantum chemical calculations. The stabilization of the diberyllium species is rationalized from the formation of the real Be-Be single bonds with bond distances as 2.077 and 2.058 Å and binding energies as -27.1 and -77.2 kcal/mol calculated at CCSD (T)/aug-cc-pVTZ level of theory for BeBeNCCH3 and CNBeBeCH3, respectively. EDA-NOCV analysis described the interaction between Be2 and NC···CH3 fragments as Lewis "acid-base" interactions. In the complexes, the Be2 moiety carries positive charges which transfer from antibonding orbital of Be2 to the bonding fragments significantly strengthen the Be-Be bonds that are corroborated by AIM, LOL and NBO analyses. In addition, mono beryllium products BeNCCH3, CNBeCH3, HBeCH2CN and HBeNCCH2 have also been observed in our experiments.

Structural and spectroscopic characterization of large boron heterocyclic radicals: Matrix infrared spectroscopy and quantum chemical calculations

Six boron heterocyclic radicals with different conformations or configurations were synthesized in solid neon and identified by matrix isolation infrared spectroscopy as well as quantum-chemical calculations. The ground-state boron atom selectively attacks the C = C bond of cycloheptene forming η2 (1,2)-BC7H12 complex (A), which contains a chair conformation and a boat conformation. Species A isomerizes to the 2,3,4,5,6,7-hexahydroborocine radical (B), which involves an eight-membered boron heterocyclic ring and also has two isomers observed. The 1-(prop-1-en-1-yl)-2,3,4-dihydro borole radical (C) with E-configuration and Z-configuration is generated as the final product under UV light irradiation through ring contraction reaction and the hydrogen atom transfer reaction. The observation of species A and further photo-isomerization to species C is consistent with theoretical predictions that these reactions are thermodynamically exothermic and kinetically facile. This work not only provides a possible route for future design and synthesis of corresponding borole derivatives, but also provides new insights into the structural and spectroscopic information of boron heterocyclic radicals with different conformations and configurations.

Isotopic effect in thermodynamic properties of solid neon

Isotopic effects in mean-square displacement, specific heat at constant pressure and linear thermal expansion coefficient of solid neon have been considered using the statistical moment method in statistical mechanics. This approach allows us to study these effects including the anharmonicity of lattice vibrations. We implement calculations for 20Ne and 22Ne isotopes in temperature range from 0 K to the melting temperature (24.6 K) using Lennard-Jones potential to describe the interaction between Ne quantum particles. Our numerical results are compared with those of path-integral Monte Carlo simulations and previous experimental data showing the good agreement. This research presents an effective statistical approach to study isotopic effects in thermodynamic quantities of materials.

Photoelectron Spectroscopy Confirms the Gas-Phase Stability of the C3O2- Anion.

The carbon suboxide anion with an asymmetric zigzag structure, C3O2-, which was recently characterized in a solid neon matrix, has not been observed in the gas phase. Here, we have experimentally generated C3O2- in a supersonic plasma jet expansion and studied it by negative ion photoelectron spectroscopy. A spectral analysis based on the calculated Franck-Condon factors, in combination with quantum chemical calculations, has for the first time yielded a determination of the electron affinity of the neutral carbon suboxide, EA = +0.48(8) eV. Molecular orbital (MO) analysis indicates that, upon linear-to-zigzag geometric change, additional σ-π MO mixing significantly reduces the energy of the singly occupied MO of C3O2- and thus stabilizes the negative ion in the gas phase. This work provides a benchmark understanding of the gas-phase stability of the C3O2- anion.

Vibrationally resolved electronic spectroscopy of rhodamine B cation at less than 5 K: combining gas phase absorption and matrix isolation fluorescence spectroscopy

Helium tagging photodissociation action spectroscopy in the gas phase together with laser-induced fluorescence (LIF) spectroscopy in neon matrix has been used to probe the photophysics of electrosprayed rhodamine B cation cooled to < 5 K and studied in two different minimally perturbing environments ([RhB•He]+ as well as [RhB]+ in solid neon). Helium tagging experiments were performed using a newly developed apparatus He-TAG. LIF measurements were carried out using an improved matrix-isolation spectroscopy machine Depo-II. The resulting, partially vibrationally resolved electronic spectra of the S0→S1, resp. S1→S0 transition provide benchmarks for gauging the theoretical description of this prototypical organic dye. As a first approach, we have compared our spectra to TD-DFT-based predictions of vibronic structure at the Franck-Condon (FC) and Franck-Condon Herzberg-Teller (FCHT) levels. Depletion action and fluorescence spectroscopy of rhodamine B cation at < 5 K

Matrix infrared spectroscopic and ab initio investigations of methylamine-CO2 and methylamine-CO2-water complexes

For the first time the investigation of methylamine (CH3NH2)-CO2 and methylamine-CO2-water complexes in solid neon was performed in the far- and mid- infrared range FTIR spectroscopy. From concentration effects and with the help of theoretical harmonic calculations performed at the second-order Møller-Plesset level we have identified several vibrational transitions for CH3NH2-CO2 and CH3NH2-CO2-water complexes. In the CH3NH2-CO2-water complex the methylamine and water molecules interact through hydrogen bonding where the water plays the role of the proton donor. Comparison between experimental and theoretical data allows us to deduce structures of observed complexes in solid neon.

Boron-Mediated C–C and C≡N Bond Cleavage of Acetonitrile: Matrix Infrared Spectra and Theoretical Calculations

The reactions of laser-ablated B atoms with acetonitrile in 4 K solid neon have been investigated by matrix-isolation infrared spectra, and new products have been identified by 10B, D, and 13C isotopic substitutions and quantum chemical calculations. The side-on complex B-η2-(NC)-CH3 was observed during deposition and isomerized to NCBCH3, CNBCH3, and CNB(H)═CH2, respectively, through C–C bond breakage and hydrogen transfer. For diboron reaction with acetonitrile, the N-end-on complex BBNCCH3 was formed on deposition, which rearranged to HBNC(B)═CH2 and HBNBC═CH2 by λ > 220 nm irradiation. In this reaction pathway, the C≡N triple bond was completely cleaved. The final diboron product HBNBC═CH2 was much more stable than the precursors by 152.0 kcal mol–1 at the CCSD(T)-Full/cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory.

Dynamics of Electronically Excited Metal Atoms (Zn and Cd) in Rare Gas Matrices: Simulation of Multiple-band Emission using Molecular Dynamics with Quantum Transitions.

Molecular dynamics with quantum transitions approach is employed to simulate the spectroscopic characteristics of the 1 P1 ↔1 S0 transitions in atomic zinc and cadmium in order to gain insight into the excited state behavior of these atoms isolated in solid rare gases neon, argon, and krypton. The absorption and emission spectra are simulated. Non-radiative processes play a fundamental role in the transfer of population among the three electronic states initially accessed in absorption. Three distinct relaxation pathways were identified. Two of these are related to the dynamical modes described in previous works [McCaffrey and Kerins, J. Chem. Phys. 106, 7885 (1997); Kerins and McCaffrey, J. Chem. Phys. 109, 3131 (1998)] in which the system evolves to form a square planar configuration around the metal atom. The third distinct pathway involves motion on a hexagonal close packed plane. The temperature dependence of complex formation was also determined for the three relaxation pathways.

Cascade production of secondary electrons and photons and energy absorption mechanisms in liquid nitrogen irradiated by photons in the energy range of 0.027–17.4 keV

Mechanisms of absorption and redistribution of energy in liquid nitrogen irradiated by 0.027–17.4 keV photons are studied by Monte Carlo simulation, accurately accounting for the cascade relaxation of inner-shell vacancies and tracking all secondary electrons and photons. Densities of energy absorbed near the sites of initial photoionization due to inelastic processes caused by secondary electrons and photons and their spectra are calculated. The absorption of energy by the sample’s atoms that underwent initial ionization by incident photons is only important on a rather narrow incident photon energy interval in the UV range. With growing incident photon energy, the energy absorbed in primary photoionization acts decreases and becomes negligible in comparison with energy absorbed via other mechanisms. The main mechanism of energy transfer to the sample (average of 56% over the whole incident photon energy interval) is through secondary electrons causing ionization and excitation of atoms of the medium. The second most important energy absorption mechanism (22%) is by low-energy photons that do not produce ionization or excitation of the sample’s atoms. Low-energy secondary electrons are responsible for the absorption of 14% of energy, and 7% of the absorbed energy is transferred to the medium through photoionization by secondary photons. Low-energy electrons are produced in great quantities in liquid nitrogen after each primary photoionization act, and their number grows linearly against incident photon energy. The results of this study are in line with earlier reported results on energy absorption in photon-irradiated disordered solid neon, amorphous carbon, and water.

Phosphorus-Boron Multiple Bonding in the π Radical HBP.

The HBP radical was generated via the reaction of laser ablated boron atom with PH3 in a solid neon matrix, which is identified via IR spectroscopy with isotopic substitutions and quantum chemical calculations. The results show that HBP has a 2 Π electronic ground state with a short B-P bond. Bonding analysis indicates that besides an electron-sharing σ bond, there are two degenerate π bonding orbitals that are occupied by three electrons, resulting in a bond order of two and half between P and B. This is in sharp contrast to the bonding properties of the isovalent HNB, which was characterized to be a N≡B triply bonded σ radical with the unpaired electron locating on the B atom.

Nitrogen Trifluoride Complexes of Group 10 Transition Metals M(NF3) (M = Pd, Pt).

The group 10 transition metal atoms Pd and Pt react with nitrogen trifluoride (NF3) forming N-coordination M(NF3) complexes in solid neon and argon matrices. The M(NF3) complexes isomerize to more stable fluoronitrenoid FNMF2 isomers via fluorine migration upon blue LED (λ = 470 nm) light irradiation. These products are characterized on the basis of infrared absorption spectroscopy with isotopic substitutions and theoretical frequency calculations. The analysis of the electronic structure of nitrogen trifluoride complexes indicates that the bonding between metal and nitrogen trifluoride can be described as σ donation from the HOMO of nitrogen trifluoride to the empty metal dz2 orbital and π back-donation from the metal dxz/yz orbitals to the LUMO of nitrogen trifluoride, the latter of which stabilized the metal ligand bond and destabilized the ligand N-F bond. In FNMF2, the FN ligand doubly bonded to the metal and bear imido character.